Typically, glass fibers are formed by drawing molten glass into filaments through a bushing or orifice plate and applying a sizing composition containing lubricants, coupling agents, and film-forming binder resins to the filaments. The aqueous sizing composition provides protection to the fibers from interfilament abrasion and promotes compatibility between the glass fibers and any matrix in which the glass fibers are to be used for reinforcement purposes. After the sizing composition is applied, the fibers may be gathered into one or more strands and wound into a package or, alternatively, the fibers may be chopped while wet and collected. The collected chopped strands can then be dried and cured to form dry use chopped strand glass (DUCS), or they can be packaged in their wet condition as wet use chopped strand glass (WUCS). Such chopped glass fiber strands are commonly used as reinforcement materials in thermoplastic articles. It is known in the art that glass fiber reinforced polymer composites possess higher mechanical properties compared to unreinforced polymers. Thus, better dimensional stability, tensile strength and modulus, flexural strength and modulus, impact resistance, and creep resistance can be achieved with glass fiber reinforced composites.
Fibrous mats, which are one form of fibrous non-woven reinforcements, are extremely suitable as reinforcements for many kinds of synthetic plastic composites. The two most common methods for producing glass fiber mats from chopped glass fibers are wet-laid processing and dry-laid processing. Generally, in a conventional wet-laid process, the chopped fibers are dispersed in a water slurry which may contain surfactants, viscosity modifiers, defoaming agents, or other chemical agents. Once the chopped glass fibers are introduced into the slurry, the slurry is agitated so that the fibers become dispersed. The slurry containing the fibers is then deposited onto a moving screen, and a substantial portion of the water is removed to form a web. A binder is then applied, and the resulting mat is dried to remove the remaining water and cure the binder. The formed non-woven mat is an assembly of dispersed, individual glass filaments. Wet-laid process are commonly used when a very uniform distribution of fibers is desired.
Conventional dry-laid processes include processes such as an air-laid process and a carding process. In a conventional air-laid process, dried chopped glass fibers are air blown onto a conveyor or screen and consolidated to form a mat. For example, dry chopped fibers and polymeric fibers are suspended in air, collected as a loose web on a screen or perforated drum, and then consolidated to form a randomly oriented mat. In a conventional carding process, a series of rotating drums covered with fine wires and teeth comb the glass fibers into parallel arrays to impart directional properties to the web. The precise configuration of the drums will depend on the mat weight and fiber orientation desired. The formed web may be parallel-laid, where a majority of the fibers are laid in the direction of the web travel, or they can be random-laid, where the fibers have no particular orientation.
Dry-laid processes are particularly suitable for the production of highly porous mats and are suitable where an open structure is desired in the resulting mat to allow the rapid penetration of various liquids or resins. However, such conventional dry-laid processes tend to produce mats that do not have a uniform weight distribution throughout their surface areas, especially when compared to mats formed by conventional wet-laid processes. In addition, the use of dry-chopped input fibers can be more expensive to process than the fibers used in a wet-laid process because the fibers in a dry-laid process are typically dried and packaged in separate steps before being chopped.
For certain reinforcement applications in the formation of composite parts, it is desirable to form fiber mats in which the mat includes an open, porous structure (as in a dry-laid process) and which has a uniform weight (as in a wet-laid process). Therefore, there exists a need in the art for a cost-effective and efficient process for forming a non-woven mat which has a substantially uniform weight distribution, and which has an open, porous structure that can be used in the production of reinforced composite parts that overcomes the disadvantages of conventional wet-laid and dry-laid processes.